This invention relates to a novel process for producing copolymers using homopolymers as the starting materials. More specifically, this novel process involves reacting a mixture of two or more polyamides, especially poly(caproamide) (nylon 6) and poly(hexamethylene adipamide) (nylon 6.6) and a phosphite promoter or a combination of phosphite promoters in order to obtain a copolymer from the reaction of the individual homopolymers. The materials obtained by this process are not strictly random or block copolymers but behave similarly to a random system and, therefore, we classify them as "quasi-random" copolymers. For simplicity, we shall refer to them as random copolymers. The random copolymers of the present invention may be fabricated into films or other products which have desirable properties, and can be useful in making injection molded or extruded products of improved properties.
U.S. Pat. No. 3,509,107 (Brignac, 1970) discloses a process for increasing the relative viscosity of polyamide fibers or copolyamides by incorporating a phosphorous or phosphite compound into the polyamide under an inert gas atmosphere. The primary object to Brignac is to provide a process for increasing the viscosity of polyamide yarn and cord which requires a minimum amount of inert gas. U.S. Pat. No. 3,551,548 (Brignac et al., 1970) describes various optimizing procedures for U.S. Pat. No. 3,509,107. The described patents are each directed only to a method of producing polyamide yarn with increased viscosity via incorporating a phosphorous or phosphite compound into the yarn, and then heating said yarn in the presence of inert gas.
British Pat. No. 569,184 discloses a method for producing a random copolymer from nylon 6 and nylon 6.6. The invention described therein teaches that heating a mixture of nylon 6 and nylon 6.6 results in interchange between various sections of the respective polymer molecules with the final product being a random copolymer of nylon 6 and nylon 6.6. In order to produce a random copolymer of nylon 6 and nylon 6.6, British Pat. No. 569,184 teaches that it is necessary to heat the mixture of homopolymers for periods of time up to 8 hours at 285.degree. C. without any catalyst.
Copending, commonly assigned application Ser. Nos. 280,563, 280,564, and 337,800 were filed previously, but arose from a common research program with the present invention. They are discussed herein without admitting such applications or the inventions claimed therein as being prior art with respect to the invention of this application.
Application Ser. No. 280,564 (July 6, 1981) discloses a process for decreasing the melt index and increasing the viscosity of polyamide fibers via incorporating a phosphate compound into the polyamide and heating the polyamide until the desired changes in the melt index and viscosity occur. The phosphates utilized in application Ser. No. 280,564 include substituted aryl phosphates which satisfy certain Hammett sigma values.
Application Ser. No. 280,563 (July 6, 1981) teaches that polymers of caprolactam with increased viscosity may be produced by reacting in the melt a phosphite compound and a caprolactam polymer.
Application Ser. No. 337,800 discloses a process for preparing block and graft copolymers. The described process involves reacting two or more polyamides, polyesters, acid homopolymers of .beta.-unsaturated carboxylic acids in order to form a graft and/or block copolymer. Included in the application are copolymers formed from poly(caproamide) and poly(hexamethylene adipamide).